1. Field of the Invention
This invention relates to a liquid crystal projector and a control method for a liquid crystal projector, and more particularly to a liquid crystal projector and a control method for a liquid crystal projector suitable for use to display a three-dimensional image.
2. Description of the Related Art
An image shown on a screen in a movie theater was heretofore taken using a film and shown from the film. Recently, however, as is called digital cinema, an image is recorded in the form of a digital signal and transmitted as an image signal to individual movie theaters, and in each movie theater, the image is shown on a screen using the image signal.
In the theater, the digital image signal transmitted thereto is reproduced, for example, by a liquid crystal projector which uses a liquid crystal device to project an image, and is displayed as an image on the screen.
In recent years, images shown on a screen in a movie theater include 3D contents captured so as to display a three-dimensional stereoscopic image (hereinafter referred to simply as 3D image).
In related art, where it is intended to use a liquid crystal projector to project a 3D image, popularly a technique which uses two liquid crystal projectors is adopted as disclosed, for example, in Japanese Patent Laid-Open No. Hei 8-331602. In this instance, one of the projectors projects an image for the right eye while the other projector projects an image for the left eye.
In recent years, also it has been attempted to use a single liquid crystal projector to project a 3D image.
A method in related art wherein a single liquid crystal projector is used to project a 3D image is described with reference to FIGS. 1 to 3. In other words, in the method described with reference to FIGS. 1 to 3, a 3D image is projected using a method similar to an ordinary method wherein a two-dimensional image (2D image) is projected.
FIG. 1 shows an example of a configuration of a 3D image projection system for projecting a 3D image.
Referring to FIG. 1, in the 3D image projection system, an image signal for the left eye (L side) and an image signal for the right eye (R side) as an image signal of a 3D image for a digital cinema are supplied in a cycle of 24 Hz to a liquid crystal projector 1.
Forwardly of the liquid crystal projector 1 in a direction in which the liquid crystal projector 1 projects an image, an optical shutter 2 and a polarizing element 3 are disposed. The optical shutter 2 blocks or passes light or an image from the liquid crystal projector 1, and the polarizing element 3 polarizes the light incoming thereto to a polarization direction corresponding to the L side or the R side. Usually, a liquid crystal element is used for the optical shutter 2 and the polarizing element 3.
In the liquid crystal projector 1, images corresponding to image signals for the R side and the L side are successively written into a liquid crystal panel 1A, and the images written on the liquid crystal panel 1A are projected by a light source not shown. In particular, light of the images emitted from the liquid crystal projector 1 passes through the optical shutter 2 and is polarized to a predetermined polarization direction by the polarizing element 3 and then displayed on a screen 4.
A user can wear polarizing glasses 5 and watch a 3D image as light of the image for the left eye enters the left eye and light of the image for the right eye enters the right eye.
Incidentally, it is necessary for a liquid crystal device to be driven by AC driving wherein the polarity of the application voltage is inversed with predetermined timings in a unit of one screen image or the like so that the integrated value of DC components may be zero in order to prevent deterioration of the liquid crystal substance and so forth. In the following, one of the polarities of the application voltage is referred to as normal polarity while the other polarity opposite to the normal polarity is referred to as inversed polarity.
For example, where the liquid crystal projector 1 successively displays 2D images A, B and C in a time series, it stacks image signals of the images A, B and C successively supplied thereto in a cycle of 24 Hz into an internal memory and writes the images A, B and C into the liquid crystal panel 1A in such a manner as seen in FIG. 2A to display the images A, B and C. In particular, the image A is first written into the liquid crystal of the liquid crystal panel 1A with the application voltage set to the normal polarity to display the image A, and then the image A is written into the liquid crystal of the liquid crystal panel 1A with the application voltage set to the inversed polarity to display the image A. Then, also when the next image B is to be displayed, the liquid crystal projector 1 first writes the image B into the liquid crystal of the liquid crystal panel 1A with the application voltage set to the normal polarity to display the image B, and then writes the image B into the liquid crystal of the liquid crystal panel 1A with the application voltage set to the inversed voltage to display the image B. This similarly applies also to the image C.
Accordingly, if it is tried to display a 3D image in accordance with the same method as that for the display of a 2D image, then the liquid crystal projector 1 first displays a first image L1 on the L side with the application voltage set to the normal polarity with a certain timing and then displays the first image L1 with the application voltage set to the inversed polarity as seen in FIG. 2B. Then, with a next timing, the liquid crystal projector 1 displays a first image R1 on the R side with the application voltage set to the normal polarity and then displays the image R1 with the application voltage set to the inversed polarity.
The image or panel image written into the liquid crystal panel 1A, the driving polarity representative of whether the polarity of the application voltage then is the normal polarity or the inversed polarity, the opening/closing operation of the optical shutter 2 and the polarization direction of the polarizing element 3 have such a relationship as seen from FIG. 3.
After the image L1 is written within T1 time into the liquid crystal panel 1A with the application voltage set to the normal polarity, the image L1 is written into the liquid crystal panel 1A with the application voltage set to the inversed polarity within T2 time. Further, within the T2 time, the optical shutter 2 is opened and the polarization direction of the polarizing element 3 is controlled to that for the left eye. Since the image written into the liquid crystal panel 1A within the T2 time is same as the image written within the T1 time, there is no problem even if the optical shutter 2 remains open while the image L1 is written into the liquid crystal panel 1A within the T2 time.
Within T3 time next to the T2 time, the image R1 is written into the liquid crystal panel 1A with the application voltage set to the normal polarity and the optical shutter 2 is closed to block the light from the liquid crystal projector 1. This is because, within the T3 time, both of the image R1 written newly and the preceding image L1 exist in the liquid crystal panel 1A. Then, within T4 time, the optical shutter 2 is opened and the polarization direction of the polarizing element 3 is controlled to that for the right eye, and the image R1 is written into the liquid crystal panel 1A with the application voltage set to the inversed polarity.
A period of time within which a series of image L1 (normal), image L1 (inversed), image R1 (normal) and image R1 (inversed) are displayed, that is, the total time period of the T1 time to the T4 time, corresponds to one cycle of 24 Hz.
In this manner, the liquid crystal projector 1 in related art uses image signals for the L side and the R side supplied thereto in a cycle of 24 Hz and projects the images in order of the image L (normal), image L (inversed), image R (normal) and image R (inversed) to the screen 4 to display a 3D image.